Bridge relays (or "bridges" for short) are Tor relays that aren't listed in
the main Tor directory. Since there is no complete public list of them, even if
your ISP is filtering connections to all the known Tor relays, they probably
won't be able to block all the bridges. If you suspect your access to the
Tor network is being blocked, you may want to use bridges.

The addition of bridges to Tor is a step forward in the blocking
resistance race. It is perfectly possible that even if your ISP filters
the Internet, you do not require a bridge to use Tor. So you should try
to use Tor without bridges first, since it might work.

Note that it's also possible that Tor is non-functional for other
reasons. The latest version of
Tor Browser tries to give you better hints about why Tor is having
problems connecting. You should also read the
FAQ about problems with running Tor properly when you have issues.
If you feel that the issue is clearly related to Tor being blocked, or
you'd simply like to try because you're unsure or feeling adventurous,
please read on. Ensure that you're using the latest
Tor Browser for your platform.

To use a bridge, you have two options. Tor Browser now provides some
bridges by default. You can enable these easily. Unfortunately, because
these bridges are publically distributed, it is easy for censors to block
some of them, so some of them may not work. In this case, you'll need to
locate different bridges. Furthermore, you'll need to configure Tor Browser
with whichever bridge address you intend to use. If your Internet connection
requires the use of a proxy, you'll probably need to configure Tor Browser
to use it first. If you don't think you need to configure a proxy for your
Internet connection, you probably don't. Give it a try and if you have
issues, ask us for help.

Over the last few years, censors have found ways to block Tor even when
clients are using bridges. They usually do this by installing special
boxes at ISPs that peek into network traffic and detect Tor; when Tor
is detected they block the traffic flow.

To circumvent such sophisticated censorship Tor introduced
pluggable transports.
These transports manipulate all Tor traffic between the client and its
first hop such that it is not identifiable as a Tor connection. If the
censor can't decide if the connection is a Tor connection, then they are
less likely to block it.

Sadly, pluggable transports are not immune to detection, if a censor
is given enough time. In the past, we promoted obfs and obfs2 as safe
transports. These are now deprecated and were replaced by obfs3,
scramblesuit, fte, and obfs4.

Bridges which support pluggable transports can be used with Tor Browser
easily. Tor Browser includes some pre-configured bridges and you can get
more from BridgeDB, if those don't work.

As an example, when you obtain a bridge from https://bridges.torproject.org,
you'll get a bridge entry that looks like the following:

141.201.27.48:443 4352e58420e68f5e40bf7c74faddccd9d1349413

Understanding the components of a bridge line isn't strictly required
but may prove useful. You can skip this section if you'd like.
The first element is the IP address of the bridge: '141.201.27.48'
The second element is the port number: '443'
The third element, the fingerprint (unique identifier of the
bridge), is optional:
'4352e58420e68f5e40bf7c74faddccd9d1349413'

Pluggable transports tip:

If your bridge line looks like this:

obfs3 141.201.27.48:420 4352e58420e68f5e40bf7c74faddccd9d1349413

The first element is the name of the pluggable transport
technology used by the bridge. For example, in the case above, the
bridge is using the obfs3 pluggable transport.

1) To add a bridge, follow the instructions on screen. Click the
"Configure" button.

2) If you must configure a proxy then select "Yes" and enter the
details on the following page.
If you do not use a proxy then select "No" and click "Next".
If you do not know if you must configure a proxy then you likely
do not need to do it.

3) After you configure a proxy or skip over that configuration page,
the following page asks "Does your Internet Service Provider (ISP)
block or otherwise censor connections to the Tor Network?". Select
"Yes" and then click "Next".

4) Now you have two configuration options. You can use bridges which are
preconfigured and provided with Tor Browser, or you can specify your
own bridge(s).

5a) If you want to use one of the provided bridges, then choose the
transport type you want to use. obfs3 is currently the recommend
type, but depending on where you are located another type may work better
for you. If you have any questions, please contact
us.

5b) Alternatively, if you want to use a custom
bridge, then select "Enter custom bridges" and copy-and-paste the
bridge information into the textbox.

6) After you decide which bridges you want to use, click "Connect".
Tor should now be able to load successfully and the browser window
should appear.

The following instructions assume Tor Browser successfully loads and
you are able to surf the web. If you do not see the web browser when you
run Tor Browser (like in step (1) below), you may need to follow the
instructions above.

1) Start Tor Browser:

2) To begin using bridges, open Tor Browser's Network Settings:

4) Now you have two configuration options. You can use bridges which are
preconfigured and provided with Tor Browser, or you can specify your
own bridge(s).

5a) If you want to use one of the provided bridges, then choose the
transport type you want to use. obfs3 is currently the recommend
type, but depending on where you are located another type may work better
for you. If you have any questions, please contact
us.

5b) Alternatively, if you want to use a custom
bridge, then select "Enter custom bridges" and copy-and-paste the
bridge information into the textbox.

Tor will only use one bridge at a time, but it is good to add more than one
bridge so you can continue using Tor even if your first bridge becomes
unavailable.

You can also get bridges by sending mail to bridges@bridges.torproject.org
with the line "get bridges" by itself in the body of the mail. You'll need
to send this request from a Gmail, Riseup!, or Yahoo! account, though
— we only accept these providers because otherwise we make it too
easy for an attacker to make a lot of email addresses and learn about all
the bridges. Almost instantly, you'll receive a reply that includes:

Similarly, if you need bridges with a specific pluggable transport, the
process is just as easy. First, decide which type you want. Currently we
provide obfs2, obfs3, scramblesuit, and fte. If you don't know which one
you should choose, then obfs3 is usually a good choice. Send an email to
bridges@bridges.torproject.org with "get transport obfs3" by itself in
the body of the email (replace "obfs3" with whichever pluggable transport
you want to use). You should receive an email like this:

When configured as a bridge, your server will not appear in the public
Tor network.

Your bridge relay will automatically publish its address to the bridge
authority, which will give it out via https or email as above.
You can construct the bridge address
using the format above (you can find the
fingerprint in your Tor log files or in /var/lib/tor/fingerprint
depending on your platform).

If you would like to learn more about our bridge
design from a technical standpoint, please read the Tor bridges
specification. If you're interested in running an unpublished bridge
or other non-standard uses, please do read the specification.